Thanks a lot for submitting the patch, I'm eager to see emacs-next in
upstream!
However, there is a potential issue with it. Original emacs package that we
inherit here sets EMACSLOADPATH with two values, one of which is some
directory path combined with the version:
https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/emacs.scm?h=master#n196

Every Emacs version creates a dir along the lines of
.gix-profile/share/emacs/version/lisp. Current emacs from master hardcodes
this version to 27.0.50, so this path becomes
.gix-profile/share/emacs/27.0.50/lisp. But since we set version based on
commit in this submitted patch, EMACSLOADPATH becomes invalid and this
specific directory doesn't end up in the guix-profile/etc/profile script,
so when you run emacs, you get multiple errors because Emacs can't load
builtin packages. I think that hardcoding a version of emacs-next to
"27.0.50" should work well. I'm attaching a patch that can be applied to
Amin's emacs-next patch.

Regards,
Valentin